There is a worldwide interest in capturing and sequestering or reusing carbon dioxide (CO2) emissions to stabilize the climate. Aqueous amine processes, widely used throughout the natural gas industry to reduce CO2 from gas streams via chemical reaction, represent the benchmark by which CO2 capture technologies are evaluated (NETL, Carbon Sequestration Technology Roadmap and Program Plan (2007); Rochelle, G. T., “Amine Scrubbing for CO2 Capture,” Science, 325:1652-1654 (2009)). While effective at reducing CO2 from gas streams, amine processes are highly energy intensive, with much of the energy penalty attributed to boiling water during amine regeneration. Thus, aqueous amine processes will inherently suffer from large energy penalties. However, new solvents with little or no volatility can provide the desired energy efficiency.
Ionic liquids have received significant attention as solvents for CO2 capture (Bara, J. E., et al., “Guide to CO2 Separations in Imidazolium-based Room-Temperature Ionic Liquids,” Ind. Eng. Chem. Res., 48:2739-2751 (2009)). As ionic liquids do not evaporate, they potentially offer greatly improved energy efficiency. However, the use of ionic liquids for CO2 capture has not been scaled due to limitations of their physical and thermodynamic properties. Issues with ionic liquids consistently cited are very low CO2 loading, high viscosity, and exceedingly high costs (NETL, Existing Plants, Emissions and Capture—Setting CO2 Program Goals, DOE/NETL-2009/1366). Inclusion of amine functionalities within the ionic liquid (i.e., “task-specific” ionic liquids) or blending ionic liquids with commodity amines such as monoethanolamine (MEA) greatly improves the CO2 capacity of the solvent and also reduces the energy requirement (NETL, Existing Plants, Emissions and Capture—Setting CO2 Program Goals, DOE/NETL-2009/1366; Camper, D. et al., “Room-Temperature Ionic Liquid—Amine Solutions: Tunable Solvents for Efficient and Reversible Capture of CO2,” Ind. Eng. Chem. Res., 47:8496-8498 (2008)). While using ionic liquid-amine blends is promising, alternative volatile solvents that overcome the viscosity and cost limitations of ionic liquids are needed.